Toast bread in 350°F oven until golden brown, about 5 minutes.
Rub lightly with garlic clove while still warm.
Coarsely chop the mushrooms .
In a large skillet heat 2 tablespoons oil over moderate heat until hot but not smoking and cook mushrooms until softened, then add shallots and garlic stirring, until all liquid mushrooms give off is evaporated, about 5 minutes. Season with salt and pepper. Remove skillet from heat. Keep mushrooms warm, covered.
This can be made ahead,refrigerated and reheated at serving time.
Quarter tomatoes; combine with red onion, basil, vinegar, olive oil. Season, to taste, and let marinate for 15 minutes.
Top toasted bread with Sauteed mushrooms, tomato relish, shaved parmesan. Garnish with basil.